The mystery is even greater given that Karin Bergman, who kept extensive diaries, recording both events and thoughts, was by all accounts unaware that Ingmar was not the child to whom she gave birth July 14,1918 but a surrogate child. [. . .]
The analysis, which reached her April 12, 2011, established with certainty that Ingmar Bergman was not the son of Karin Bergman, supporting Tillberg’s hypothesis about her own family. It is not yet certain who Bergman’s mother was, but a great deal of circumstantial evidence suggests that it was Tillberg’s grandmother, Hedvig Sjöberg (later Tillberg), who in July 1918 gave birth to a son in Stockholm who was immediately given up for adoption.
DNA tests show Ingmar Bergman not his mother's biological child
Who was the mother of Ingmar Bergman?